TRANSISTOR AS A SWITCH - WORKING






WORKING OF TRANSISTOR AS A SWITCH


The process of applying DC voltages across the different terminals of a transistor is called Biasing. For normal operation the emitter-base junction is always forward biased while the collector base junction is reverse biased.

Lets look how

TRANSISTOR ACT AS A SWITCH



bjt as a switch principle




The switching action of a bipolar junction transistor can be explained easily with the help of its output characteristics. Transistor mainly works on mainly three regions


ACTIVE

SATURATION

CUTOFF


TRANSISTOR IS IN ON CONDITION WHEN IT IS IN SATURATION MODE. And in OFF state when transistor is in CUTOFF REGION. When a transistor is working as a switch,the cutoff and saturation regions are the stable regions of its operation,while active region is the unstable state To make a transistor in off mode,
make
Vce=Vcc in common emitter configuration,
where Vcc is the supply voltage and Vce is the voltage across collector-emitter terminal.

Simillarly, to make Transistor ON we have to give or maintain 0V across the collector emitter junctions.

ie; Vce=0V



It means Collector and Emitter junctions get short circuited (0V) so the current conducts from collector to emitter.



Other useful posts:-



Base width Modulation and Early effect


Biasing and operating modes of Transistors




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